Setup OpenVPN server and client

Introduction

Want to access the Internet safely and securely from your smartphone or laptop when connected to an untrusted network such as the WiFi of a hotel or coffee shop? A Virtual Private Network (VPN) allows you to traverse untrusted networks privately and securely as if you were on a private network. The traffic emerges from the VPN server and continues its journey to the destination.

When combined with HTTPS connections, this setup allows you to secure your wireless logins and transactions. You can circumvent geographical restrictions and censorship, and shield your location and any unencrypted HTTP traffic from the untrusted network.

OpenVPN is a full-featured open source Secure Socket Layer (SSL) VPN solution that accommodates a wide range of configurations. In this tutorial, we'll set up an OpenVPN server on a Droplet and then configure access to it from Windows, OS X, iOS and Android. This tutorial will keep the installation and configuration steps as simple as possible for these setups.

Prerequisites

To complete this tutorial, you will need access to an Ubuntu 16.04 server.

You will need to configure a non-root user with sudo privileg ces before you start this guide.
When you are ready to begin, log into your Ubuntu server as your sudo user and continue below.

Step 1: Install OpenVPN

To start off, we will install OpenVPN onto our server. OpenVPN is available in Ubuntu's default repositories, so we can use apt for the installation. We will also be installing the easy-rsa package, which will help us set up an internal CA (certificate authority) for use with our VPN.

Step 2: Set Up the CA Directory

OpenVPN is an TLS/SSL VPN. This means that it utilizes certificates in order to encrypt traffic between the server and clients. In order to issue trusted certificates, we will need to set up our own simple certificate authority (CA).

To begin, we can copy the easy-rsa template directory into our home directory with the make-cadir command:

make-cadir ~/openvpn-ca

Move into the newly created directory to begin configuring the CA:

cd ~/openvpn-ca

Step 3: Configure the CA Variables

To configure the values our CA will use, we need to edit the vars file within the directory. Open that file now in your text editor:

nano vars

Inside, you will find some variables that can be adjusted to determine how your certificates will be created. We only need to worry about a few of these.

Towards the bottom of the file, find the settings that set field defaults for new certificates. It should look something like this:

Step 4: Build the Certificate Authority

Now, we can use the variables we set and the easy-rsa utilities to build our certificate authority.

Ensure you are in your CA directory, and then source the vars file you just edited:

cd ~/openvpn-ca
source vars

You should see the following if it was sourced correctly:

Output
NOTE: If you run ./clean-all, I will be doing a rm -rf on /home/sammy/openvpn-ca/keys

Make sure we're operating in a clean environment by typing:

./clean-all

Now, we can build our root CA by typing:

./build-ca

This will initiate the process of creating the root certificate authority key and certificate. Since we filled out the vars file, all of the values should be populated automatically. Just press ENTER through the prompts to confirm the selections:

Output
Generating a 2048 bit RSA private key
..........................................................................................+++
...............................+++
writing new private key to 'ca.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [US]:
State or Province Name (full name) [NY]:
Locality Name (eg, city) [New York City]:
Organization Name (eg, company) [DigitalOcean]:
Organizational Unit Name (eg, section) [Community]:
Common Name (eg, your name or your server's hostname) [DigitalOcean CA]:
Name [server]:
Email Address [admin@email.com]:

We now have a CA that can be used to create the rest of the files we need.

Step 5: Create the Server Certificate, Key, and Encryption Files

Next, we will generate our server certificate and key pair, as well as some additional files used during the encryption process.

Start by generating the OpenVPN server certificate and key pair. We can do this by typing:

Note: If you choose a name other than server here, you will have to adjust some of the instructions below. For instance, when copying the generated files to the /etc/openvpn directroy, you will have to substitute the correct names. You will also have to modify the /etc/openvpn/server.conf file later to point to the correct .crt and .key files.

./build-key-server server

Once again, the prompts will have default values based on the argument we just passed in (server) and the contents of our vars file we sourced.

Feel free to accept the default values by pressing ENTER. Do not enter a challenge password for this setup. Towards the end, you will have to enter y to two questions to sign and commit the certificate:

Next, we'll generate a few other items. We can generate a strong Diffie-Hellman keys to use during key exchange by typing:

./build-dh

This might take a few minutes to complete.

Afterwards, we can generate an HMAC signature to strengthen the server's TLS integrity verification capabilities:

openvpn --genkey --secret keys/ta.key

Step 6: Generate a Client Certificate and Key Pair

Next, we can generate a client certificate and key pair. Although this can be done on the client machine and then signed by the server/CA for security purposes, for this guide we will generate the signed key on the server for the sake of simplicity.

We will generate a single client key/certificate for this guide, but if you have more than one client, you can repeat this process as many times as you'd like. Pass in a unique value to the script for each client.

Because you may come back to this step at a later time, we'll re-source the vars file. We will use client1 as the value for our first certificate/key pair for this guide.

To produce credentials without a password, to aid in automated connections, use the build-key command like this:

cd ~/openvpn-ca
source vars
./build-key client1

If instead, you wish to create a password-protected set of credentials, use the build-key-pass command:

cd ~/openvpn-ca
source vars
./build-key-pass client1

Again, the defaults should be populated, so you can just hit ENTER to continue. Leave the challenge password blank and make sure to enter y for the prompts that ask whether to sign and commit the certificate.

Step 7: Configure the OpenVPN Service

Next, we can begin configuring the OpenVPN service using the credentials and files we've generated.

Copy the Files to the OpenVPN Directory

To begin, we need to copy the files we need to the /etc/openvpn configuration directory.

We can start with all of the files that we just generated. These were placed within the ~/openvpn-ca/keys directory as they were created. We need to move our CA cert and key, our server cert and key, the HMAC signature, and the Diffie-Hellman file:

Next, find the section on cryptographic ciphers by looking for the commented out cipher lines. The AES-128-CBC cipher offers a good level of encryption and is well supported. Remove the “;” to uncomment the cipher AES-128-CBC line:

The settings above will create the VPN connection between the two machines, but will not force any connections to use the tunnel. If you wish to use the VPN to route all of your traffic, you will likely want to push the DNS settings to the client computers.

You can do this, uncomment a few directives that will configure client machines to redirect all web traffic through the VPN. Find the redirect-gateway section and remove the semicolon “;” from the beginning of the redirect-gateway line to uncomment it:

This should assist clients in reconfiguring their DNS settings to use the VPN tunnel for as the default gateway.
(Optional) Adjust the Port and Protocol

By default, the OpenVPN server uses port 1194 and the UDP protocol to accept client connections. If you need to use a different port because of restrictive network environments that your clients might be in, you can change the port option. If you are not hosting web content your OpenVPN server, port 443 is a popular choice since this is usually allowed through firewall rules.

If you have no need to use a different port, it is best to leave these two settings as their default.
(Optional) Point to Non-Default Credentials

If you selected a different name during the ./build-key-server command earlier, modify the cert and key lines that you see to point to the appropriate .crt and .key files. If you used the default server, this should already be set correctly:

Adjust the UFW Rules to Masquerade Client Connections

If you followed the Ubuntu 16.04 initial server setup guide in the prerequisites, you should have the UFW firewall in place. Regardless of whether you use the firewall to block unwanted traffic (which you almost always should do), we need the firewall in this guide to manipulate some of the traffic coming into the server. We need to modify the rules file to set up masquerading, an iptables concept that provides on-the-fly dynamic NAT to correctly route client connections.

Before we open the firewall configuration file to add masquerading, we need to find the public network interface of our machine. To do this, type:

ip route | grep default

Your public interface should follow the word “dev”. For example, this result shows the interface named wlp11s0, which is highlighted below:

Output
default via 203.0.113.1 dev wlp11s0 proto static metric 600

When you have the interface associated with your default route, open the /etc/ufw/before.rules file to add the relevant configuration:

sudo nano /etc/ufw/before.rules

This file handles configuration that should be put into place before the conventional UFW rules are loaded. Towards the top of the file, add the highlighted lines below. This will set the default policy for the POSTROUTING chain in the nat table and masquerade any traffic coming from the VPN:

Note: Remember to replace wlp11s0 in the -A POSTROUTING line below with the interface you found in the above command.

Open the OpenVPN Port and Enable the Changes

Next, we'll adjust the firewall itself to allow traffic to OpenVPN.

If you did not change the port and protocol in the /etc/openvpn/server.conf file, you will need to open up UDP traffic to port 1194. If you modified the port and/or protocol, substitute the values you selected here.

We'll also add the SSH port in case you forgot to add it when following the prerequisite tutorial:

sudo ufw allow 1194/udp
sudo ufw allow OpenSSH

Now, we can disable and re-enable UFW to load the changes from all of the files we've modified:

sudo ufw disable
sudo ufw enable

Our server is now configured to correctly handle OpenVPN traffic.

Step 9: Start and Enable the OpenVPN Service

We're finally ready to start the OpenVPN service on our server. We can do this using systemd.

We need to start the OpenVPN server by specifying our configuration file name as an instance variable after the systemd unit file name. Our configuration file for our server is called /etc/openvpn/server.conf, so we will add @server to end of our unit file when calling it:

sudo systemctl start openvpn@server

Double-check that the service has started successfully by typing:

sudo systemctl status openvpn@server

If everything went well, your output should look something that looks like this:

First, locate the remote directive. This points the client to our OpenVPN server address. This should be the public IP address of your OpenVPN server. If you changed the port that the OpenVPN server is listening on, change 1194 to the port you selected:

# SSL/TLS parms.# See the server config file for more# description. It's best to use# a separate .crt/.key file pair# for each client. A single ca# file can be used for all clients.#ca ca.crt#cert client.crt#key client.key

Mirror the cipher and auth settings that we set in the /etc/openvpn/server.conf file:

Finally, add a few commented out lines. We want to include these with every config, but should only enable them for Linux clients that ship with a /etc/openvpn/update-resolv-conf file. This script uses the resolvconf utility to update DNS information for Linux clients.

If your client is running Linux and has an /etc/openvpn/update-resolv-conf file, you should uncomment these lines from the generated OpenVPN client configuration file.

Save the file when you are finished.

Creating a Configuration Generation Script

Next, we will create a simple script to compile our base configuration with the relevant certificate, key, and encryption files. This will place the generated configuration in the ~/client-configs/files directory.

Create and open a file called make_config.sh within the ~/client-configs directory:

Step 11: Generate Client Configurations

Now, we can easily generate client configuration files.

If you followed along with the guide, you created a client certificate and key called client1.crt and client1.key respectively by running the ./build-key client1 command in step 6. We can generate a config for these credentials by moving into our ~/client-configs directory and using the script we made:

cd ~/client-configs
./make_config.sh client1

If everything went well, we should have a client1.ovpn file in our ~/client-configs/files directory:

ls ~/client-configs/files

Output
client1.ovpn

Transferring Configuration to Client Devices

We need to transfer the client configuration file to the relevant device. For instance, this could be your local computer or a mobile device.

While the exact applications used to accomplish this transfer will depend on your choice and device's operating system, you want the application to use SFTP (SSH file transfer protocol) or SCP (Secure Copy) on the backend. This will transport your client's VPN authentication files over an encrypted connection.

Here is an example SFTP command using our client1.ovpn example. This command can be run from your local computer (OS X or Linux). It places the .ovpn file in your home directory:

sftp sammy@openvpn_server_ip:client-configs/files/client1.ovpn ~/

Step 12: Install the Client Configuration

Now, we'll discuss how to install a client VPN profile on Windows, OS X, iOS, and Android. None of these client instructions are dependent on one another, so feel free to skip to whichever is applicable to you.

The OpenVPN connection will be called whatever you named the .ovpn file. In our example, this means that the connection will be called client1.ovpn for the first client file we generated.

Windows

Installing

The OpenVPN client application for Windows can be found on OpenVPN's Downloads page. Choose the appropriate installer version for your version of Windows.

Note
OpenVPN needs administrative privileges to install.

After installing OpenVPN, copy the .ovpn file to:

C:\Program Files\OpenVPN\config

When you launch OpenVPN, it will automatically see the profile and makes it available.

OpenVPN must be run as an administrator each time it's used, even by administrative accounts. To do this without having to right-click and select Run as administrator every time you use the VPN, you can preset this, but this must be done from an administrative account. This also means that standard users will need to enter the administrator's password to use OpenVPN. On the other hand, standard users can't properly connect to the server unless the OpenVPN application on the client has admin rights, so the elevated privileges are necessary.

To set the OpenVPN application to always run as an administrator, right-click on its shortcut icon and go to Properties. At the bottom of the Compatibility tab, click the button to Change settings for all users. In the new window, check Run this program as an administrator.

Connecting

Each time you launch the OpenVPN GUI, Windows will ask if you want to allow the program to make changes to your computer. Click Yes. Launching the OpenVPN client application only puts the applet in the system tray so that the VPN can be connected and disconnected as needed; it does not actually make the VPN connection.

Once OpenVPN is started, initiate a connection by going into the system tray applet and right-clicking on the OpenVPN applet icon. This opens the context menu. Select client1 at the top of the menu (that's our client1.ovpn profile) and choose Connect.

A status window will open showing the log output while the connection is established, and a message will show once the client is connected.

Disconnect from the VPN the same way: Go into the system tray applet, right-click the OpenVPN applet icon, select the client profile and click Disconnect.

OS X

Installing

Tunnelblick is a free, open source OpenVPN client for Mac OS X. You can download the latest disk image from the Tunnelblick Downloads page. Double-click the downloaded .dmg file and follow the prompts to install.

Towards the end of the installation process, Tunnelblick will ask if you have any configuration files. It can be easier to answer No and let Tunnelblick finish. Open a Finder window and double-click client1.ovpn. Tunnelblick will install the client profile. Administrative privileges are required.

Connecting

Launch Tunnelblick by double-clicking Tunnelblick in the Applications folder. Once Tunnelblick has been launched, there will be a Tunnelblick icon in the menu bar at the top right of the screen for controlling connections. Click on the icon, and then the Connect menu item to initiate the VPN connection. Select the client1 connection.

Linux

Installing

If you are using Linux, there are a variety of tools that you can use depending on your distribution. Your desktop environment or window manager might also include connection utilities.

The most universal way of connecting, however, is to just use the OpenVPN software.

On Ubuntu or Debian, you can install it just as you did on the server by typing:

sudo apt-get update
sudo apt-get install openvpn

On CentOS you can enable the EPEL repositories and then install it by typing:

sudo yum install epel-release
sudo yum install openvpn

Configuring

Check to see if your distribution includes a /etc/openvpn/update-resolv-conf script:

ls /etc/openvpn

Output
update-resolve-conf

Next, edit the OpenVPN client configuration file you transfered:

nano client1.ovpn

Uncomment the three lines we placed in to adjust the DNS settings if you were able to find an update-resolv-conf file:

This should connect you to your server.
To make openvpn autoconnect on boot, copy the .ovpn file to /etc/openvpn and rename it to .conf

Rename the .ovpn file to .conf and move it to /etc/openvpn/ and a daemon will be started for it at boot time

Step 13: Test Your VPN Connection

Once everything is installed, a simple check confirms everything is working properly. Without having a VPN connection enabled, open a browser and go to DNSLeakTest.

The site will return the IP address assigned by your internet service provider and as you appear to the rest of the world. To check your DNS settings through the same website, click on Extended Test and it will tell you which DNS servers you are using.

Now connect the OpenVPN client to your Droplet's VPN and refresh the browser. The completely different IP address of your VPN server should now appear. That is now how you appear to the world. Again, DNSLeakTest's Extended Test will check your DNS settings and confirm you are now using the DNS resolvers pushed by your VPN.

Step 14: Revoking Client Certificates

Occasionally, you may need to revoke a client certificate to prevent further access to the OpenVPN server.

To do so, enter your CA directory and re-source the vars file:

cd ~/openvpn-ca
source vars

Next, call the revoke-full command using the client name that you wish to revoke:

./revoke-full client3

This will show some output, ending in error 23. This is normal and the process should have successfully generated the necessary revocation information, which is stored in a file called crl.pem within the keys subdirectory.

Transfer this file to the /etc/openvpn configuration directory:

sudo cp ~/openvpn-ca/keys/crl.pem /etc/openvpn

Next, open the OpenVPN server configuration file:

sudo nano /etc/openvpn/server.conf

At the bottom of the file, add the crl-verify option, so that the OpenVPN server checks the certificate revocation list that we've created each time a connection attempt is made: